The present invention relates to a duct produced from non-woven material by thermoforming, especially an air intake duct for an internal-combustion engine. This type of duct formed by thermoforming is produced by welding, longitudinal edge to longitudinal edge, two semicylinders by means of two flanges projecting from the outer surface of the semicylinders. It is often necessary to form, at a certain point along the longitudinal extension of this type of duct, a portion of the duct in the form of bellows. In the conventional designs of cylindrical ducts, these bellows allow the duct to bend along any bending axis, whether in the XZ plane or YZ plane, Z being defined as the longitudinal axis of the cylinder and X, Y defining a transverse plane. However, with ducts formed by compression moulding, by welding two semicylinders edge to edge along the two longitudinal flanges projecting from the outer surfaces of the two semicylinders, the bending in the plane parallel to the plane in which the two flanges lie, that is to say a twist with respect to an axis perpendicular to the plane in which the two flanges lie, is no longer possible because of the stiffness of the two flanges.
As a result, for example in the case of an intake duct, it is more difficult to install this type of intake duct and the path along which it is installed must in particular be less complex. This is because it is less easy to follow sinuous trajectories.
The present invention aims to overcome this drawback by providing a duct formed by compression moulding, made of non-woven material, especially polyester, which although being formed by compression moulding and having two longitudinal flanges projecting from its upper surface, may however be bent with respect to any bending axis.
According to the invention, the thermoformed intake duct made of non-woven material and including flanges parallel to the longitudinal axis of the duct, projecting from the outer surface of the duct, a first portion of the duct being formed in the form of a first bellows, a first bellows-shaped portion having two longitudinal flanges diametrically opposed along a first diameter, characterized in that the duct includes at least a second bellows-shaped portion having two longitudinal flanges diametrically opposed along a second diameter of the duct which makes, with respect to the first diameter of the two flanges of the first bellows-shaped portion, a non-zero angle, and especially 90xc2x0.
By thus providing two bellows portions offset with respect to each other, the possibility of bending the duct whether at the first portion, for example for bending it with respect to a given axis, or at the second bellows portion, in order to bend it with respect to the axis in which it was not possible to bend the first portion, may be obtained. The duct with two bellows-shaped portions may thus be bent in any direction and be easily installed in an engined vehicle in the same way as a flangeless intake duct.
According to a preferred embodiment of the invention, two bellows portions are welded together so as to be adjacent, one beside the other.